Dynamoelectric machines such as motors and generators and other rotating machines such as gears and bearing systems are widely employed in industrial and commercial facilities. These machines are relied upon to operate with minimal attention and provide for long, reliable operation. Many facilities operate several hundred or even thousands of such machines concurrently, many of which are integrated into a large interdependent process or system. Like most machinery, at least a small percentage of such equipment is prone to failure. Some of such failures can be attributed to loss of lubrication, incorrect lubrication, lubrication breakdown or lubrication contamination.
Depending on the application, the failure of a machine in service can possibly lead to system or process down time, inconvenience, material scrap, machinery damage, hazardous material cleanup and possibly even a dangerous situation. Thus, it is desirable to diagnose the machinery for possible failure or faults early in order to take preventive action and avoid such problems. Absent special monitoring for certain lubrication problems, the problem may have an insidious effect in that although only a minor problem on the onset, the problem could become serious if not detected. For example, bearing problems due to inadequate lubrication, lubrication contamination or other causes may not become apparent until significant damage has occurred.
Proper lubrication facilitates the extension of machinery life. For example, when motor lubricant is continuously exposed to high temperatures, high speeds, stress or loads, and an oxidizing environment, the lubricant will deteriorate and lose its lubricating effectiveness. The loss of lubricating effectiveness will affect two main functions of a lubrication system, namely: (1) to reduce friction; and (2) to remove heat. Continued operation of such a degraded system may result in even greater heat generation and accelerated system degradation eventually leading to substantial machinery damage and ultimately catastrophic failure. To protect the motor, the lubricant should be changed in a timely fashion. However, a balance must be struck--on one hand it is undesirable to replace an adequate lubricant but on the other hand it is desired to replace a lubricant that is in its initial stages of breakdown or contamination before equipment damage occurs. Since each particular application of a lubricant is relatively unique with respect to when the lubricant will breakdown or possibly become contaminated, it becomes necessary to monitor the lubricant.
Various techniques for analyzing lubricants are known. For example, measuring a dielectric constant change in the lubricant or recording a thermal history of the lubricant have been employed for monitoring the lubricant's condition. However, these methods measure a single parameter and require the use of the same lubricant or assume no machinery malfunctions throughout the measurements. Furthermore, these monitoring techniques are generally not performed in situ and typically require that a sample of the lubricant be extracted and analyzed using laboratory grade equipment to determine the condition of the lubricant. The need to monitor and determine the current and future health of lubricants include grease and oils such as used in bearing systems for motors, gears, pillow blocks, hydrodynamic bearings as well as hydraulic fluids such as found in pumps and pump systems, and cutting fluids to name a few.
Single parameter sensors only provide a narrow view of a lubricant quality and/or health. Accurate lubricant health assessment and lifetime prediction is virtually impossible to achieve via sensing a single parameter of the lubricant. The need for more information about the lubricant is readily apparent from the many parameters which are reported in a typical laboratory report of lubricant condition.
In view of the above, there is a need for an improved sensor for detecting an operating state of a lubricant.